Materials such as amalgam and silicate cement have hitherto been used as dental filling materials. These materials, however, have no adhessiveness to tooth substance but have liability to cause secondary caries. Further, some uncertainty with regard to durability and fear of injuriousness to the pulp or soft tissues have compelled these materials to be replaced by resin type filling materials. In other words, a monomer to be used as the dental filling material is a mixture of polymethyl methacrylate and metyl methacrylate, of bisphenol-A glycidyl dimethacrylate and ethyleneglycol dimethacrylate, or of urethane dimethacrylate, 2,2-di-(4-methacryloxy ethoxy phenol)propane and triethylene glycol dimethacrylate. Such mixture is incorporated with fillers such as silica power and amines such as dimethyl-p-toluidine and p-tolyldiethanolamine, as well as peroxides such benzoyl peroxide. Then, the resulting mixture is polymerized by amine-peroxide system to form the filling materials.
As well-known in the art, however, such monomer has a C--C homo bond in its chain and skeleton and therefore produces a polymer of high flexibility and bending, but has disadvantages of high thermal expansion coefficient and low heat-resistance. In other words, the resulting polymer is low in strength and hardness, large in polymerization shrinkage and low in softening point. Consequently, if the above-mentioned mixture of monomers is filled into dental cavities, gaps may be produced between cavities and polymers due to polymerization shrinkage and temperature change upon eating and drinking, thereby to cause secondary caries. In addition, the polymer has poor hardness and strength, resulting in ready wearability and poor durability.